1. Field of the Invention
The present invention concerns a liquid crystal element, and particularly, it relates to a liquid crystal element that can be utilized suitably as to a guest-host type liquid crystal element.
2. Description of the Related Art
With the spread of the digital technology, the importance of a paper type display for displaying digital information (hereinafter referred to as “electronic paper”) has been increasing. The performance required for the electronic paper includes a high visual recognition and a low electric power consumption. High visual recognition means white background similar to paper, and hence a display method based on light-scattering white background similar to paper is suited. On the other hand, as to the electric power consumption, the reflection type display system has a lower power consumption as compared with that of self light-emission display system. Many systems have been proposed so far for the electronic paper. Examples include a reflection type liquid crystal display system, electrophoresis display system, magnetophoresis display system, dichroic ball rotation system, electrochromic display system, and leucothermal system. Any of these methods is not satisfactory from the viewpoint of high visual recognition, and improvement therefore has been demanded.
For the liquid crystal element (liquid crystal display element), various systems have already been proposed, and a light shutter effect has usually been utilized for the coloration of the liquid crystal element by providing red, blue, and green mosaic color filters to a liquid crystal panel, putting the liquid crystal panel between two polarizing plates, and changing the alignment direction of liquid crystals by switching on/off of a voltage. However, in this method, transmittance is decreased extremely by the color filters to result in extremely dark display.
In view of the above, a guest-host type liquid crystal element has received attention, and the method is promising as a liquid crystal element capable of bright display and suitable to reflection type display. In the guest-host type liquid crystal element, a liquid crystal composition in which a dichroic dye is dissolved in the liquid crystal is sealed in a cell, an electric field is applied, and alignment of the dichroic dye is changed along with the movement of the liquid crystals according to the electric field to change the light absorption state of the cell and thereby conduct display.
Since the liquid crystal element scarcely absorbs light in a state where the liquid crystals are aligned in the direction parallel with the electric field (direction toward the side of observation), achromatic display is possible. Accordingly, display in a wide color reproduction range is possible by laminating liquid crystal compositions containing dichroic dyes of different absorption wave lengths. However, independent addressing thereof involves a problem in that the structure is extremely complicated due to, for example, the requirement of providing an electrode for each of the layers.
On the other hand, as a method of addressing a plurality of liquid crystal layers independently by using one pair of electrodes, a method of using dual frequency addressable nematic liquid crystal and addressing in low frequency and high frequency regions while changing the state of the initial alignment of each liquid crystal layer has been disclosed, for example, in Japanese Patent Application Laid-Open (JP-A) No. 5-216018, etc. However, the liquid crystal element described above involves problems in that the color reproduction range is narrow due to the color combination of a complimentary color relationship and in that the state can not be maintained when the voltage application is stopped, thereby there is no memory property.
Accordingly, it has been desired to provide a liquid crystal element and a color display method capable of addressing respective liquid crystal layers independently by one pair of electrodes and having a memory property. Further, since such a technique would also be useful in a case where a dye is not contained (colorless), the reflective index could be changed in the depth direction, and the reflective index could be modulated freely by one pair of electrodes, it could be applied, for example, to reflective index modulating material or a material for changing an image depending on the viewing angle.